Improve cinder CLI existing tests

Objective of this patch to parse the output of read only cinder CLI's,
to validate the output and improve more output verification.
It is improving the code of all below read only cinder CLI's subcommands:
1. backup-list
2. extra-specs-list
3. list
4. rate-limits
5. snapshot-list
6. type-list
7. credentials
8. availability-zone-list
9. endpoints
10. service-list
11. transfer-list
12. qos-list
13. encryption-type-list

Partially implements: blueprint cli-tests-coverage

Change-Id: I3fbbc44194898b9a699a9807a7a800e9a9cb925d
1 file changed